A system utilizing rabbit adrenal cell suspensions is being developed to use in the determination of the mechanism of the action of ACTH in stimulating an increase in adrenal 17 alpha-hydroxylase activity. The ability of inhibitors of RNA, DNA, protein and heme biosynthesis to block this stimulation will be investigated, as will the ability of cAMP to mimic the action of ACTH. The possibility of prostaglandin mediation of the stimulation will also be studied. By using adrenal microsome preparations from ACTH-stimulated and control animals, we will attempt to demonstrate whether an increase in cytochrome P450 accompanies the increase in 17 alpha-hydroxylase activity. The substrate binding difference spectra in these preparations will also be measured in an effort to demonstrate a correlation with the increase in 17 alpha-hydroxylation. By these investigations we hope to further the understanding of the role of tropic hormone in regulating enzyme activity.